The present invention relates generally to signal amplifiers, and more particularly to radio frequency (RF) signal power amplifiers for use in radio communication systems.
Prior art RF signal power amplifiers, such as those amplifiers described in U.S. Pat. Nos. 3,471,796, 3,652,948 and 3,714,597, typically have been constructed by utilizing discrete circuit elements, which must be carefully arranged on conventional printed circuit boards in order to assure operability. However, such RF signal power amplifiers are difficult to manufacture because of the need for fine tuning adjustments which are accomplished by adding hand-selected trimming components. The discrete circuitry type of RF signal power amplifiers have been utilized for amplifying RF signals having frequencies in the 20 MHz to 200 MHz range.
At higher operating frequencies, for example, frequencies in the 400-500 MHz range, RF signal power amplifiers may practically utilize microstrip transmission line techniques, since the wavelength of RF signals at these frequencies and corresponding lengths of the microstrip transmission line circuitry are relatively short. RF signal power amplifiers utilizing microstrip transmission line circuitry are described in U.S. Pat. No. 3,671,878 and in Motorola Instruction Manual No. 68P81017E40, entitled "Base and Repeater Stations", published by Motorola Service Publications Department, Motorola, Inc., Schaumburg, Ill., 1972. The use of microstrip transmission line techniques in RF signal power amplifiers becomes even more attractive as the frequency of the RF signal increases. For example, in the 800-900 MHz frequency range, microstrip transmission line techniques have been utilized in an RF signal power amplifier described in Motorola Instruction Manual No. 68P81030E10, entitled "Cell Site RF Power Amplifier", published by Motorola Service Publications, Motorola, Inc., Schaumburg, Ill., 1975. However, none of the foregoing prior art RF signal power amplifiers utilizing either discrete circuitry techniques or microstrip transmission line techniques provide a high degree of spurious signal rejection, while at the same time, providing for simple and inexpensive manufacturability by minimizing the number of hand assembly operations.